Comparison of leaf litter ant communities in woodlands, lowland forests and montane forests of north-eastern Tanzania

Ants were extracted in Winkler bags from sifted leaf litter sampled in arange of forest and woodland types in and around Mkomazi Game Reserve innorth-eastern Tanzania, including the Eastern Arc Mountains of South Pare andWest Usambara. A total of 87 ant species were recorded, of which 32.2% were onlyrecorded from montane forests (1400–1850 m altitude), 6.9%only from lowland forest (540–810 m), 19.5% only fromwoodland (300–1080 m), and 16.1% in all three forest types.Of the 28 species recorded only from montane forests, 12 species were only foundin the Mkomazi forests, four only in the Pares and seven species only in theUsambaras. Sites of similar altitude grouped together in a cluster analysis, andspecies richness decreased with an increase in altitude. The lowland forest andclosed woodland sites did not form distinct communities. To ensure preservationof ant species, forests from a full range of altitudes need to be conserved.This study confirms the status of the West Usambara forests as having a highlyendemic biota, and the critical need to adequately conserve the remainingvestiges of montane forest within Mkomazi Game Reserve.     

Structural comparison of tropical montane rain forests along latitudinal and altitudinal gradients in south and east Asia

Geographical patterns of altitudinal zonation, floristic composition, and structural features of tropical montane rain forests were examined along latitudinal gradients in south and east Asia. On equatorial mountains, the tropical montane rain forests occur above 1000 m. Toward middle latitudes, they come farther down and reach sea level at c. 35° N. Thus, the forests are equivalent to the subtropical rain forests of the latitudinal, horizontal zonation series. They exhibit gradual changes in floristic composition and structure along both altitudinal and latitudinal gradients. On equatorial mountains, they are divided into three types, i.e. tropical lower montane, upper montane, and subalpine forests. The three tree regeneration types, having emergent, sporadic and inverse-J type stem-diameter class frequency distributions, coexist in the lower montane forests, but the upper and subalpine forests display only the inverse-J type species with a few species of the sporadic type. Toward the northern latitudinal limit, the distinction between the three tropical montane forest zones in equatorial mountains becomes less clear. This can be explained by temperature conditions: on equatorial mountains, a temperature sum of 85° C months which controls the upper limit of the lower montane forests, and a coldest month mean temperature of-1° C which controls the evergreen broad-leaved trees, appear at c. 2500 and c. 4000 m respectively. The altitudinal range between 2500 m and 3800 m, which is the upper forest limit, is covered by upper montane and subalpine forests. On the other hand, at the latitudinal northern limit, the tropical upper montane and subalpine forests cannot exist because the above mentioned two temperature conditions occur at nearly the same point. Thus, at the northern latitudinal limit of the tropical montane forests, the three zones of equatorial mountains amalgamate into a single subtropical lowland forest community. This is due to the seasonal temperature climate in middle latitudes in, e.g., central Japan and central China.A part of this paper was presented as an oral presentation at the Vth International Congress of Ecology, Yokohama 23–30.8.1990.     

Environmental correlates of gastrointestinal parasitism in montane and lowland baboons in Natal,South Africa

We compared the gastrointestinal parasites of the baboon,Papio cynocephalus ursinus, living in montane (altitude, >1800 m) and coastal lowland (altitude, 100–200 m) habitats in Natal, South Africa, using fecal analysis. While the montane animals harbored a smaller number of species, helminth egg-output rates were higher in them than in the lowland animals. The decrease in parasite diversity with increasing altitude was expected, but the difference in helminth egg output was not. It may be due to a combination of food shortage, which characterizes the montane environment, especially at the end of winter, and the high proportion of soil-contaminated items in the diets of the montane animals.     

Lekking birds in a tropical forest forego sex for migration

Facultative, partially migratory animals provide a contemporary window into the evolution of migration, offering rare opportunities to examine the life-history trade-offs associated with migration. For the first time, to our knowledge, we describe the nature of these trade-offs, using a lek-breeding tropical bird, the white-ruffed manakin (Corapipo altera). Previous evidence indicated that weather drives post-breeding migration to lower elevations bringing condition-related benefits. Using elevation-sensitive stable isotope measurements and more than 1200 h of behavioural observations, we show that male manakins which migrate incur costs of diminished social status and matings with females the following breeding season. Because migratory tendency depends on inter-annual variation in weather, physical costs of displays and breeding prospects the following year, migratory decisions are subject to both natural and sexual selection, with the outcome of such decisions linked to changing climatic regimes.     

Assessing the effects of selective logging on birds in Neotropical piedmont and cloud montane forests

In tropical and subtropical forests there is limited information about how to integrate sustainable timber management with the conservation of biodiversity. We examined the effect of selective logging on the bird community to help develop management guidelines to assure the conservation of biodiversity in forests managed for timber production. The study design consisted of control and harvested plots in piedmont and cloud forests of the subtropical montane forests of the Andes in northwestern Argentina. We conducted bird point-count surveys combined with distance estimation. Breeding season bird community composition was more similar between control and logged forest in both the cloud forest and piedmont, than between the two elevations, probably because Neotropical bird communities change dramatically along elevational gradients. Within each elevation zone, community composition changed significantly between harvested and control forests. Both between and within each elevation zone no significant differences in bird density were detected. Similarly, when we analyzed bird density according to diet guilds no general pattern could be extracted. However, we found a significantly greater density of cavity nesters and lower of non-cavity nesters in control plots, probably because most trees that can develop suitable cavities were extracted in logged plots and these plots had a greater structural diversity enabling more nesting resources. Grouping species according to their nesting habitat requirements has rarely been used in the neotropics and other tropical and subtropical forests, but focusing management attention on cavity nesters might address the most sensitive portion of the avian community as well as other species dependent on trees likely to hold cavities.     

Assemblage and population-level consequences of forest fragmentation on bilateral asymmetry in tropical montane birds

Habitat fragmentation has the potential to influence the development and thus the phenotype of organisms. The asymmetry of bilateral traits may be indicative of the extent to which developmental stability is compromised by the stressful conditions underlying fragmentation. Using an assemblage- and population-level approach, we explored asymmetry differences in tarsus and outermost tail feathers of birds inhabiting fragmented landscapes in the tropical Andes of Colombia. More than 2500 individuals of 185 species were mist-netted at nine forest sites representing continuous forest (> 1000 ha), medium- (70–110 ha), and small-sized (8–20 ha) fragments. Feathers showed true fluctuating asymmetry (FA), whereas tarsus presented a mixture of FA and directional asymmetry. Overall, asymmetry was lowest in continuous forest, and highest in small and medium fragments. These patterns remained unchanged when directionality and differences in species composition, abundance, and foraging tactics were considered. The population-level analyses showed a general trend of increased asymmetry variation in fragments, yet the responses were not always in the same direction. Increased asymmetry may represent an outcome of processes that contribute to the persistence of species in changing environments, and to the generation of phenotypic innovation, which suggests individual adjustments of development to deal with stress. This calls into question the deliberated application of FA as a biomonitoring tool for conservation.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 119–133.     

Diversification across an altitudinal gradient in the Tiny Greenbul (Phyllastrephus debilis) from the Eastern Arc Mountains of Africa

Background  

The Eastern Arc Mountains of Africa have become one of the focal systems with which to explore the patterns and mechanisms of diversification among montane species and populations. One unresolved question is the extent to which populations inhabiting montane forest interact with those of adjacent lowland forest abutting the coast of eastern Africa. The Tiny Greenbul (Phyllastephus debilis) represents the only described bird species within the Eastern Arc/coastal forest mosaic, which is polytypic across an altitudinal gradient: the subspecies albigula (green head) is distributed in the montane Usambara and Nguru Mountains whereas the subspecies rabai (grey head) is found in Tanzanian lowland and foothill forest. Using a combination of morphological and genetic data, we aim to establish if the pattern of morphological differentiation in the Tiny Greenbul (Phyllastrephus debilis) is the result of disruptive selection along an altitudinal gradient or a consequence of secondary contact following population expansion of two differentiated lineages.     

The natural link between Europe and Africa – 2.1 billion birds on migration

The Palaearctic–African migration system comprises enormous numbers of birds travelling between Europe and Africa twice each year. Migratory birds may form strong links between the two continents given they can act as both transport vehicles for parasites and diseases as well as temporary consumers with increased food demand to fuel their flight. Knowing the number of migrating birds is crucial if such links are to be quantified. We estimate that today approximately 2.1 billion songbirds and near-passerine birds migrate from Europe to Africa in autumn, 73% of which are accounted for by just 16 species. This number is only half the estimate from the 1950s in the only other assessment to date. The discrepancy is mainly caused by the limited information on population sizes in the past. Our estimated number of migrants is highly dependent on the accuracy of the underlying estimates of breeding population sizes, as well as breeding parameters in species with relatively high reproductive output. The updated figures quantify and emphasize the strong natural connection between Africa and Europe, which has important implications for manifold research topics including those related to climate change, human health and biological conservation.     

Human activity facilitates altitudinal expansion of exotic plants along a road in montane grassland,South Africa

Question: Do anthropogenic activities facilitate the distribution of exotic plants along steep altitudinal gradients? Location: Sani Pass road, Grassland biome, South Africa. Methods: On both sides of this road, presence and abundance of exotic plants was recorded in four 25‐m long road‐verge plots and in parallel 25 m x 2 m adjacent land plots, nested at five altitudinal levels: 1500, 1800, 2100, 2400 and 2700 m a.s.l. Exotic community structure was analyzed using Canonical Correspondence Analysis while a two‐level nested Generalized Linear Model was fitted for richness and cover of exotics. We tested the upper altitudinal limits for all exotics along this road for spatial clustering around four potential propagule sources using a t‐test. Results: Community structure, richness and abundance of exotics were negatively correlated with altitude. Greatest invasion by exotics was recorded for adjacent land at the 1500 m level. Of the 45 exotics, 16 were found at higher altitudes than expected and observations were spatially clustered around potential propagule sources. Conclusions: Spatial clustering of upper altitudinal limits around human inhabited areas suggests that exotics originate from these areas, while exceeding expected altitudinal limits suggests that distribution ranges of exotics are presently underestimated. Exotics are generally characterised by a high propagule pressure and/or persistent seedbanks, thus future tarring of the Sani Pass may result in an increase of exotic species richness and abundance. This would initially result from construction‐related soil disturbance and subsequently from increased traffic, water run‐off, and altered fire frequency. We suggest examples of management actions to prevent this.     

Effects of an ENSO-related fire on birds of a lowland tropical forest in Sumatra

Comparisons of bird community composition in burned and unburned areas of a lowland tropical rainforest in Sumatra, Indonesia indicated the following during the first 5 years after burning: (1) original burn severity strongly affected bird community composition at both the genus and family levels; (2) bird community composition continued to change progressively away from immediate post-burn composition in medium and severely burned forest as well as adjacent unburned forest; and (3) the degree of impact was both taxon and guild specific, with understory insectivores most detrimentally affected. Although species richness may temporarily increase in burned areas, this study suggests that multiple wildfires will lead to a decline in diversity over a large scale as birds of open fields replace interior forest specialists.     

Floristic similarities between lowland and montane areas of Atlantic Coastal Forest in Northeastern Brazil

Studies undertaken in the Atlantic Coastal Forest have revealed a notable floristic heterogeneity within this vegetation type in NE Brazil. However, there is still a great need for detailed comparisons of the floristic relationships between the various forest types found there. This work presents an analysis of the floristic similarity (at the species level) of these forest as revealed by floristic surveys, with the aim of better understanding and defining this vegetation. Using a binary matrix, grouping, ordering, and TWINSPAN analysis were performed on 742 tree/shrub species listed in 35 different plant surveys. These tree/shrub species were divided by these analysis into two large floristic groups – ombrophilous and semideciduous. The semideciduous group was formed, in general, by forest areas located at altitudes above 700 m (montane forests), and could itself be divided into two subgroups. The first subgroup was located more inland (Pernambuco), while the second subgroup was located nearer the coast (within the states of Pernambuco and Ceará). The ombrophilous group was quite heterogeneous, but could also be divided into two floristic subgroups: i) lowland forests (below 100 m a.s.l) in the states of Pernambuco, Paraíba, and in two areas of Bahia, as well as some montane forests (in Pernambuco, between 640 and 900 m a.s.l.); ii) lowlands forests in the states of Alagoas and Bahia. This latter subgroup is the largest and best defined, and has the highest degree of internal similarity. Nonetheless, it can be further subdivided into two smaller classes, one in Alagoas and the other in Bahia State. The results of this study demonstrate that the concept of the Atlantic Coastal Forest could also include montane ombrophilous forests in Pernambuco State, as these forests form a single floristic unit together with lowland forests in that state. This revised version was published online in June 2006 with corrections to the Cover Date.     

Spatial distribution of understory fruit-eating birds and fruiting plants in a neotropical lowland wet forest

Spatial distribution of fruit-eating birds and fruiting shrubs of the Melastomataceae and Rubiaceae were examined on a 10 ha plot in tropical lowland wet forest of Costa Rica. Many plant species and most birds exhibited considerable spatial variation in their occurrence on the plot, as indicated by the distribution patterns of shrubs with ripe fruits and captures in mist nets, respectively. In many cases, captures of fruit-eating birds were correlated with abundance of fruiting plants, particularly for species that rely heavily on fruits. In general, fruit-eating birds concentrated their use of the plot to areas rich in fruiting shrubs. This differential use of certain areas likely results in differential visitation to fruiting plants located in these areas and in a heterogeneous dissemination of seeds into the habitat.     

A study of altitudinal zonation in the montane forest belt of Mt. Elgon,Kenya/Uganda

Altitudinal changes in the vegetation of the Montane Forest Belt of Mt. Elgon, East Africa, were investigated by analysis of aerial photographs and by sample plots along two transects, one on a relatively wet, and the other on a relatively dry aspect.Classifications for both tree and herb/shrub plots show that the forests along the two transects become increasingly similar floristically with altitude. The total number of tree species recorded is greater for the transect on the moister aspect. The mean altitudinal range for tree species increases on both transects with altitude, while that for herb/shrub species remains constant. It is suggested that the upper altitudinal limits of many species are determined principally by temperature-related factors, while the degree to which species extend their ranges downwards is much influenced by competition.Structural heterogeneity is particularly well marked at altitudes corresponding to the bamboo zone on the wetter slopes and, even in the absence of bamboo, tree density here is much reduced. it is suggested that thicket-forming species, including bamboo, have enhanced competitive ability in intermediate altitude montane forests.Previously advanced classificatory schemes for montane forest vegetation in eastern Africa are examined in the light of the findings.Nomenclature follows Agnew (1974) and Dale & Greenway (1961) with minor modifications after Chapman & White (1970), Mabberley (1973) and Pennington & Styles (1975).The work was funded by a grant from the Natural Environment Research Council (U.K.). We are grateful to the Government of Kenya and to the Forest Department, Kenya, for permission to work on Mt. Elgon. Dr. A. D. Q. Agnew and Miss C. Kabuye very kindly identified some of the plant specimens. The illustrations were drawn by Mr. J. Shaw and the manuseript was critically read by Dr. D. Riley.     

Sulphur and nitrogen changes in forest soils of East Africa

Summary Sulphur measurements made on soils in East Africa revealed the unexpected occurrence of sulphates in forest subsoils. Soil profiles from plantation and natural forests were analysed and a general pattern of sulphur distribution was found.It has been found that in addition to the sulphur cycle dependent upon microbiological oxidation of organic sulphur there exists a cycle whereby sulphate is circulated as such between trees and soil.The biological oxidation of organic sulphur in the soil is an extremely slow process compared with that of carbon and nitrogen. Treatment with calcium carbonate, nitrates and non-sulphur-containing amino acids had no effect upon the subsequent sulphate production. Incubation with either S-containing amino acids or with calcium sulphate however, resulted in an increased rate of soil-sulphur oxidation and this effect is being further investigated.An aqueous extract of wattle leaves proved to inhibit nitrification in the soil for short periods and evidence is presented which suggests that methionine may be involved in this effect.     

Effects of fires on butterfly assemblages in lowland dipterocarp forest in East Kalimantan

The post‐fire butterfly fauna in lowland dipterocarp forest of the Bukit Soeharto Education Forest (BSEF), East Kalimantan, Indonesia, was assessed during the period November 1998–April 2000 by means of consecutive Malaise trap samples, with supplementary field observations for March–April 1999. A total of 514 butterflies belonging to 61 species and representing six families were caught in the traps. Melanitis leda (Nymphalidae: Satyrinae), Charaxes bernardus (Nymphalidae: Charaxinae), and Danaus genutia (Nymphalidae: Danainae) were the species most frequently caught (60, 52 and 47 individuals, respectively), representing 31% of the total. These three species are generalists and “disturbance indicators” for tropical rainforest, being characteristic of disturbed or secondary forests, being distributed widely, and having larvae that feed on a wide range of host plants. In contrast, other species, such as Trogonoptera brookiana and Troides amphrysus, were recorded before the fires but were not recorded again afterwards. The pre‐ and post‐fire butterfly fauna of East Kalimantan were compared on the basis of butterfly specimens deposited in the Tropical Rain Forest Research Center that were collected in and around the Bukit Soeharto Education Forest before the fires (1988–1995). On the basis of the post‐fire survey, based on Malaise trap samples and field observations, only 43% of the butterfly species (not including Lycaenidae and Hesperiidae) were confirmed to have persisted. The data suggest that refugia that are not affected by fire are necessary for the conservation of specialist butterflies, as well as many other forms of wildlife.     

Interdisciplinary research towards management of non-timber forest resources in lowland rain forests of Sri Lanka

Lowland and mid-elevational rainforests of Sri Lanka harbor a relict, endemic-rich flora which is also rich in timber and non-timber forest resources. These forests supply nearly half the total wood requirements of the country and are dwindling rapidly; management of the forests to conserve the biological richness and maintain environmental services is therefore a difficult proposition. This predicament is further compounded by the dependency of rural people on a range of non-timber forest resources for their subsistence and income. A forestry master plan recently prepared for Sri Lanka has not given adequate recognition to the important role played by non-timber forest resources in rural livelihood. This oversight is primarily due to the lack of quantitative information to justify the role of non-timber forest resources in forestry sector development. Forestry policies that ignore these resources often anger local people, leading the villagers to vent their disapproval through destructive actions such as burning timber plantations. Long-term interdisciplinary research in ecology, reproductive and soil biology, ethnobiology, silviculture, rural sociology and resource economics in progress at Sinharaja attempts to address these questions of sustainable development of forest resources in an integrated mode. While research oriented toward conservation investigates both short- and long-term ecosystem dynamics in natural and modified forest stands, utilization-oriented research probes the impact of increased human disturbance, particularly the impact of rural communities on dwindling forest resources, as well as the effect of forest conservation on rural livelihood. These studies continue to seek alternative methods of forest management which are socially acceptable, economically viable, and ecologically sustainable for multiple uses. These methods will assist in the refinement of current forest policies, forestry planning, and the implementation of new policies and plans in Sri Lanka.